There is considerable interest in developing sensors that act as analogs of the mammalian olfactory system (Lundstrom et al., Nature 352:47-50, 1991; Shurmer and Gardner, Sens. Act. B 8:1-11, 1992; Shurmer and Gardner, Sens. Actuators B 15:32, 1993). Such sensors have proven useful in the detection of small molecules and odorants.
Such broadly responsive sensor arrays have exploited heated metal oxide thin film resistors (Gardner et al, Sens. Act. B4:117-121, 1991; Gardner et al., Sens. Act. B 6:71-75, 1991), polymer sorption layers on the surfaces of acoustic wave resonators (Grate and Abraham, Sens. Act; B 3:85-111, 1991; Grate et al., Anal. Chem. 65:1868-1881, 1993), arrays of electrochemical detectors (Stetter et al., Anal. Chem. 58:860-866, 1986; Stetter et al., Sens. Act. B 1:43-47, 1990; Stetter et al., Anal. Chem. Acta 284:1-11, 1993), conductive polymers or composites that consist of regions of conductors and regions of insulating organic materials (Pearce et al., Analyst 118:371-377, 1993; Shurmer et al., Sens. Act. B 4:29-33, 1991; Doleman et al., Anal. Chem. 70:2560-2654, 1998; Lonergan et al., Chem. Mater. 8:2298, 1996). Arrays of metal oxide thin film resistors, typically based on tin oxide (SnO2) films that have been coated with various catalysts, yield distinct, diagnostic responses for several vapors (Corcoran et al., Sens. Act. B 15:32-37, 1993). Surface acoustic wave resonators are sensitive to both mass and acoustic impedance changes of the coatings in array elements, but the signal transduction mechanism involves somewhat complicated electronics, requiring frequency measurement to 1 Hz while sustaining a 100 MHZ Rayleigh wave in the crystal. Attempts have also been made to construct arrays of sensors with conducting organic polymer elements that have been grown electrochemically through use of nominally identical polymer films and coatings. Moreover, Pearce et al., Analyst 118:371-377, 1993; and Gardner et al., Sensors and Actuators B 18-19:240-243, 1994, describe, polypyrrole based sensor arrays for monitoring beer flavor. Shurmer (1990) U.S. Pat. No. 4,907,441, describes general sensor arrays with particular electrical circuitry. U.S. Pat. No. 4,674,320 describes a single chemoresistive sensor having a semi-conductive material selected from the group consisting of phthalocyanine, halogenated phthalocyanine and sulfonated phthalocyanine, which was used to detect a gas contaminant. Other gas sensors have been described by Dogan et al., Synth. Met 60:27-30, 1993; and Kukla, et al. Films. Sen. Act B., Chemical 37:135-140, 1996.
Measurement of air content for the detection of contaminants has become a growing concern both in the workplace (e.g., factories and laboratories), as well as in residential neighborhoods and homes. Currently, detection of hazardous chemicals or air contaminants is the result of reactions by humans and animals which are sensitive to the analyte. Upon detection, hazardous chemical teams or air-quality specialists are mobilized to the area of contamination with specialized equipment for collecting the analyte. The readings are then collected manually and often the sample is then physically taken to a separate location for analysis. These current methods require hazardous materials teams to physically enter the area and submit themselves to risks associated with the hazard.
In addition, breath testing has long been recognized as a non-intrusive medical technique that allows for diagnosis of disease or the presence of analytes. Medical symptoms of many types of conditions can be difficult to detect by medical professionals or their detection requires costly, time consuming, and highly invasive procedures often resulting in lost man hours at work, and increased risks of mortality and morbidity. Currently, medical diagnostics such as blood pressure readings and glucose readings are taken at doctors' offices or blood laboratories. The readings are then collected manually and depend on the patient's state of health at that particular time. In some cases, individuals take readings at home to assist doctors to better determine medication identification and levels. This data depends on the patient's proficiency and accuracy at taking readings, and is hard for the physician to analyze and is normally communicated only at a doctor's visit. Typically, the patient is diagnosed and medicated based on a minimum amount of data and analysis, which furthermore is not presented to the doctor in a format that facilitates diagnosis. Each reading is presented by an individual manually listing out his own readings with the date and time that these readings are taken-often in irregular intervals.
Diagnosis of many types of medical conditions, such as hypoglycemia and diabetes mellitus, can be markedly improved by a system to consolidate the data and present the data in a format which facilitates such diagnosis. In addition, remote monitoring of chemical hazard reduces the risk associated with local detection.